1. Field of the Invention
The invention is related to the field of communication networks, and in particular, to communication nodes and methods of a wireless network using a plurality of small routers to communicate over a backhaul facility.
2. Statement of the Problem
Wireless networks are comprised of a plurality of base stations, where each base station provides a service area termed a “cell”. Mobile phones in the service area of a base station are able to communicate with the base station to receive the wireless service. The base stations transmit voice, data, and signaling traffic from the mobile devices over a backhaul facility to a communication node, such as a Mobile Switching Center (MSC). The backhaul facility frequently comprises T1 lines from the base stations to the MSC. Wireless service providers often lease the T1 lines from telephone companies or cable companies. The cost of leasing the T1 lines constitutes a substantial portion of the operating budget of the service providers. Because of the cost of T1 lines, the backhaul facility is generally not configured redundantly for reliability.
Many wireless networks use Frame Relay protocol as the transport protocol over the backhaul facility. FIG. 1 illustrates a wireless network 100 using Frame Relay as the transport protocol over the backhaul facility. Wireless network 100 includes a plurality of base stations 111-113 connected to an MSC 120 over a backhaul facility 130. Although three base stations 111-113 are shown, those skilled in the art understand that MSC 120 can serve many more base stations. Backhaul facility 130 comprises a plurality of T1 lines 131-133. Wireless network 100 uses Frame Relay (FR) protocol for transporting traffic over the T1 lines 131-133. Each base station 111-113 includes a transmission interface 115-117 for terminating the T1 lines 131-133. MSC 120 includes a switch 122, such as a 5ESS switch, for terminating the T1 lines 131-133.
For each incoming T1 line, switch 122 duplicates the incoming T1 line into redundant lines for backup. One of the redundant lines is in active mode while the other line is in standby mode. The redundant lines in this architecture add reliability to wireless network 100.
Internet Protocol (IP) has been suggested as a transport protocol over the backhaul facility. FIG. 2 illustrates a wireless network 200 using IP as the transport protocol over the backhaul facility. Wireless network 200 includes a plurality of base stations 211-213 connected to an MSC 220 over a backhaul facility 230. Backhaul facility 230 comprises a plurality of T1 lines 231-233, a Digital Connect (DACS) 234, and a plurality of DS-3 lines 236-237. Each base station 211-213 includes a transmission interface 215-217 for terminating the T1 lines 231-233. MSC 220 includes two large routers 222-223 for terminating the DS-3 lines 236-237. The T1 lines 231-233 connect between DACS 234 and the transmission interfaces 215-217 in base stations 211-213. The DS-3 lines 236-237 connect between DACS 234 and large routers 222-223. Wireless network 100 uses IP for transmitting traffic over the T1 lines 131-133 and the DS-3 lines 236-237.
A large router is defined as a router that is to handle more than 10% of the traffic for MSC 220 as configured. The percentage of traffic to be handled by a router is based on the configuration of MSC 220. In FIG. 2, there are two large routers 222-223, and each large router 222-223 is assumed to handle 50% of the traffic for MSC 220 as configured (assuming reasonable load balancing between the large routers 222-223). Actual traffic handled by each of large routers 222-223 may be below the 10% level in operation, such as late at night or other low-traffic times.
One problem with the architecture for using IP over the backhaul facility 230 shown in FIG. 2 is reliability. The large routers 222-223 used in the MSC 220 do not duplicate the incoming DS-3 lines 236-237 into redundant lines for backup, as is done in switch 122 in FIG. 1 for Frame Relay. Therefore, if one of the large routers 222-223 fails, there may be a 50% traffic loss in MSC 220. A 50% traffic loss unfortunately exceeds the threshold (10%) of outage counting rules set by the TL 9000 and/or the GR 1929. For instance, TL 9000 establishes a common set of quality system requirements for suppliers of telecommunication systems, hardware, software, and services. The TL 9000 requirements include a minimum set of performance metrics and indicators to measure progress and evaluate results of quality system implementation. The TL 9000 counting rules provide that suppliers of telecommunication systems, hardware, software and services have a traffic loss no greater than 10% traffic loss. Therefore, a 50% traffic loss, as could happen in wireless network 200, would be counted as an outage.